Homolytic organometallic reactions. Part VII. An electron spin resonance study of the reaction of t-butoxyl radicals with trialkyl phosphites: kinetics of β-scission of the t-butoxytriethoxyphosphoranyl radical

Abstract

The oxidation in solution of trialkyl phosphites by t-butoxyl radicals has been studied using e.s.r. spectroscopy, and intermediate tetra-alkoxyphosphoranyl radicals [a(³¹P)ca. 900 G] have been detected. Rates of reactions (i) and (ii) were determined using e.s.r. spectroscopy to monitor the radical concentrations. Bu^tO·+ P(OEt)₃→ Bu^t·+ OP(OEt)₃(i), Bu^tOP(OEt)₃→ Bu^t·+ OP(OEt)₃(ii) The rate constants are given by the expressions log (k₁/l mol^–1 s^–1)= 9·83 – 2·24/θ and log (k_ii/s^–1)= 12·95 – 10·34/θ where θ= 2·303RT kcal mol^–1. Tetra-alkoxyphosphoranyl radicals react with oxygen to give tetra-alkoxyphosphoranylperoxyl radicals [a(³¹P)ca. 9 G] which are detected by e.s.r. at low temperatures.